Frozen-food display cases



P 1, 1964 c. E. WILLIAMS 3,146,607

FROZEN-FOOD DISPLAY GASES Filed Nov. 8. 1961 I-nvenlor CHARLES EDWARD WILLIAMS g Women United States Patent 3,146,607 FROZEN-FOOD DISPLAY CASES Charles Edward Williams, London, England, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 8, 1961, Ser. No. 151,048 Claims priority, application Great Britain Nov. 19, 1960 1 Claim. (Cl. 62-256) This invention relates to frozen-food display cases, that is to say show-cases embodying refrigeration equipment and having an open top or front to give access to goods displayed in the case.

By the present invention the refrigeration of frozen-food display cases can be more efficiently carried out.

The basis of the invention is that the display case has installed in its wall two refrigerant-evaporators, which respectively form part of two separate refrigeration systems intended to operate at different refrigerant evaporating temperatures, the lower-temperature evaporator being arranged to cool an inner part of the case wall, and the higher-temperature evaporator being arranged to cool an outer part of the wall. By such an arrangement the cooling of the case can be accomplished in two stages of refrigeration, which is more efficient. For example, with compression refrigeration, two small compressor units can give a performance which, with single-stage refrigeration of the case, would require a single compressor unit of a horse-power greater than twice the power of each of the two.

A frozen-food display case in accordance with the invention may comprise a double-wall, a refrigerant-evaporator in the inner wall, and a separate refrigerant-evaporator arranged to cool the air in the space separating the inner and outer walls, the two evaporators respectively forming part of two separate compression-refrigeration systems.

The scope of the invention is defined by the appended claim; how the invention may be performed is particularly described below with reference to the accompanying drawing, which is a vertical section from back to front through a frozen-food display case.

The example of display case shown in the drawing comprises an open-topped cabinet 1, having a doublewalled front 2, bottom 3 and rear 4. Each layer a, b of the double-wall is heat-insulated. The double-walled rear 4 is extended forwardly to form an overhang 5 partly covering the top of the case, while leaving between the edge of the overhang and the edge of the front 2 a space 6 for access to the contents. The upper portion of the front is formed by spaced glass panels 8 forming a continuation of the double wall. The ends (not shown), also, of the case 2 may be of double-walled construction; and the case 2 may be regarded as an inner heat-insulated compartment inside an outer heat-insulated container. To the outer surface of the innermost metal liner 0 of the case are secured, for example by soldering, the convolutions of a refrigerant-evaporator tube 7 of a compression refrigeration system intended to operate with a low refrigerant-evaporating temperature, say about -30 F. The remainder of this system comprises a compressor 19, a condenser 20, and connecting tubing 21, shown diagrammatically.

The intermediate space d between the inner and outer walls a, b of the front 2, bottom 3 and rear 4 is a narrow slot-like air space, which is open to the atmosphere at the edges of the top overhang 5 and of the front glass panels 8 respectively. In the part of the intermediate air space d which is in the bottom of the display case, there is separate refrigerant-evaporator tubing 9 for cooling air circulated through the intermediate space d by means "Ice of a fan 10 situated in an enlargement 11 of the air space towards the back of the bottom wall 4 of the case 2. This fan 10 acts to draw a current of air continuously through the slot-like intermediate space as indicated by arrows 12, this air being taken in at the front at the glass panels 8, between a double glass panel 13 and a single glass panel 14 drawn through the double-walled front 2 and bottom 3, into space d, where it is cooled by the evaporator 9, and impelled through the slot-like intermediate space d in the back wall 4 to emerge at the edge of the top overhang 5. The spacing between that overhang 5 and the edge of the front glass panels 8 is such that the air is projected across the access opening 6, where some at least of it is drawn in again between the glass panels 13, 14.

The evaporator tubing 7 fixed to the metal lining c of the case, and the evaporator 9 in the space d separating the layers of the bottom 3, respectively form part of separate compression-refrigeration systems intended to operate at different evaporation temperatures. The evaporator 9 is connected by tubing 22 to a compressor 23 and a condenser 24, which complete the second refrigeration system shown diagrammatically. The outer evaporator (that is the one 9 in the air space d at the bottom) would operate at a higher temperature than that of the inner evaporator 7. Thus, the cooling of the case 1 is effected in two stages: the low-temperature cooling of the metal liner 0 itself, and the cooling of the outer part of the double-wall by means of the air circulated in the space at intermediate the layers thereof. The circulating air is maintained at a temperature of perhaps +30 or 40 R, which considerably reduces the temperature differential across the insulation of the inner layer of the doublewall, and thereby reduces the amount of heat leaking in. The heat leaking through the outer layer of insulation b is picked up by the circulating air stream, which because of its relatively high temperature, permits the evaporator 9 in the bottom to operate more efficiently, and the condensing unit (not shown) connected to that evaporator can correspondingly operate at a relatively high back-pressure, such that a comparatively small refrigerating unit, say /8 H.P., can extract a substantial amount of heat at a reasonably high efficiency. The air projected from the edge of the top overhang 5 forms a curtain e of cool air, which prevents the circulation of surrounding warm air into the food-storage compartment. The front edge of the top overhang 5 has an electric light 15 on it placed above the level of the cool air curtain.

In the outer layer of the double-wall 3 forming the bottom of the case, below the evaporator 9 in the air space d, there is a drain valve 16 for allowing defrost water to be drained off. This valve comprises a light ball float 17, normally seated on a valve seat 18, but capable of being floated off that seat by an accumulation of water so that the water then drains off.

I claim:

A frozen-food display case comprising, means including vertical walls and a bottom wall for forming a partially enclosed food-storage compartment, an upper wall portion having one end thereof extending above said compartment, said vertical walls in conjunction with said upper wall portion forming a top access opening to said compartment, means forming a duct surrounding opposite ones of said vertical walls and said bottom wall, said duct having a discharge opening on one side of said top access opening and an inlet opening on the opposite side of said access opening, fan means in said duct for circulating air through said duct and from said discharge opening to said inlet opening as a high-velocity curtain of air for reducing convective interchange between air exteriorly of said frozen-food display case and the food storage compartment therein, two separate refrigeration systems each including an evaporator and a condenser, one of said evaporators having its coils located on opposite ones of said vertical walls and said top wall in substantially direct heat-transfer relationship with said compartment, the other of said evaporators having its coils located in said duct in heat-transfer contact with the outer surface of said bottom wall, said other evaporator cooling air circulated in said duct means to produce a first-stage cooling effect between the exterior of said display case and the interior food-storage compartment thereof, said one evaporator 4 serving to cool the interior food-storage compartment to a lower temperature than the air circulated in said duct.

References Cited in the file of this patent UNITED STATES PATENTS 2,706,387 Swanson Apr. 19, 1955 2,724,241 Jacobs Nov. 22, 1955 2,836,039 Weber May 27, 1958 2,923,135 Preotle Feb. 2, 1960 2,936,597 Stevens May 17, 1960 3,063,254 Dickson et al Nov. 13, 1962 

